Many mechanisms have been devised for attaching a handguard to the upper receiver of an AR-pattern firearm, including attachment to the barrel nut. In each case, the challenge is to provide a simple mechanism that secures the handguard against both axial and rotational displacement relative to the upper receiver. Some have used specialized barrel nuts that provide an attachment interface with radially oriented fasteners. Others have used clamping mechanisms, some of which draw together a longitudinal split in a rear portion of the handguard. Each of these has drawbacks and limitations in function, durability, and/or cost.